Transgenic animals are desirable for a variety of reasons, including their potential as biological factories to produce desired molecules for pharmaceutical, diagnostic and industrial uses. This potential is attractive to the industry due to the inadequate capacity in facilities used for recombinant production of desired molecules and the increasing demand by the pharmaceutical industry for use of these facilities. Numerous attempts to produce transgenic animals have met several problems, including low rates of gene incorporation and unstable gene incorporation. Accordingly, improved gene technologies are needed for the development of transgenic animals for the production of desired molecules.
Improved gene delivery technologies are also needed for the treatment of disease in animals and humans. Many diseases and conditions can be treated with gene-delivery technologies, which provide a gene of interest to a patient suffering from the disease or the condition. An example of such disease is Type 1 diabetes. Type 1 diabetes is an autoimmune disease that ultimately results in destruction of the insulin producing β-cells in the pancreas. Although patients with Type 1 diabetes may be treated adequately with insulin injections or insulin pumps, these therapies are only partially effective. Insulin replacement, such as via insulin injection or pump administration, cannot fully reverse the defect in the vascular endothelium found in the hyperglycemic state (Pieper et al., 1996. Diabetes Res. Clin. Pract. Suppl. S157-S162). In addition, hyper- and hypoglycemia occurs frequently despite intensive home blood glucose monitoring. Finally, careful dietary constraints are needed to maintain an adequate ratio of consumed calories consumed. This often causes major psychosocial stress for many diabetic patients. Development of gene therapies providing delivery of the insulin gene into the pancreas of diabetic patients could overcome many of these problems and result in improved life expectancy and quality of life.
Several of the prior art gene delivery technologies employed viruses that are associated with potentially undesirable side effects and safety concerns. The majority of current gene-delivery technologies useful for gene therapy rely on virus-based delivery vectors, such as adeno and adeno-associated viruses, retroviruses, and other viruses, which have been attenuated to no longer replicate. (Kay, M. A., et al. 2001. Nature Medicine 7:33-40).
There are multiple problems associated with the use or viral vectors. First, they are not tissue-specific. In fact, a gene therapy trial using adenovirus was recently halted because the vector was present in the patient's sperm (Gene trial to proceed despite fears that therapy could change child's genetic makeup. The New York Times, Dec. 23, 2001). Second, viral vectors are likely to be transiently incorporated, which necessitates re-treating a patient at specified time intervals. (Kay, M. A., et al. 2001. Nature Medicine 7:33-40). Third, there is a concern that a viral-based vector could revert to its virulent form and cause disease. Fourth, viral-based vectors require a dividing cell for stable integration. Fifth, viral-based vectors indiscriminately integrate into various cells and tissues, which can result in undesirable germline integration. Sixth, the required high titers needed to achieve the desired effect have resulted in the death of one patient and they are believed to be responsible for induction of cancer in a separate study. (Science, News of the Week, Oct. 4, 2002).
Accordingly, what is needed is a new vector to produce transgenic animals and humans with stably incorporated genes, which vector does not cause disease or other unwanted side effects. There is also a need for DNA constructs that would be stably incorporated into the tissues and cells of animals and humans, including cells in the resting state, which are not replicating. There is a further recognized need in the art for DNA constructs capable of delivering genes to specific tissues and cells of animals and humans.
When incorporating a gene of interest into an animal for the production of a desired protein or when incorporating a gene of interest in an animal or human for the treatment of a disease, it is often desirable to selectively activate incorporated genes using inducible promoters. These inducible promoters are regulated by substances either produced or recognized by the transcription control elements within the cell in which the gene is incorporated. In many instances, control of gene expression is desired in transgenic animals or humans so that incorporated genes are selectively activated at desired times and/or under the influence of specific substances. Accordingly, what is needed is a means to selectively activate genes introduced into the genome of cells of a transgenic animal or human. This can be taken a step further to cause incorporation to be tissue-specific, which prevents widespread gene incorporation throughout a patient's body (animal or human). This decreases the amount of DNA needed for a treatment, decreases the chance of incorporation in gametes, and targets gene delivery, incorporation, and expression to the desired tissue where the gene is needed to function.